1. Field of the Invention
The field of the present invention generally relates to methods and apparatus for continuously producing a sheet composed of a plurality of materials co-extruded in segments along the width of the sheet.
More specifically, the present invention pertains to methods and apparatus for continuously producing a thermoplastic sheet composed of a plurality of thermoplastic materials coextruded in segments, wherein at least one of the segments comprises a multi-layered thermoplastic sheet, and at least one other segment comprises a layer of a single material.
2. Description of the Prior Art
It is known in the prior art to provide methods and apparatus for co-extruding a multi-layered sheet, such as a multi-layered thermoplastic sheet. See for example U.S. Pat. Nos. 3,833,704 and 3,918,865.
U.S. Pat. No. 3,398,431 to Corbett discloses a method and apparatus for producing a laminated extruded sheet utilizing a multi-manifold die. The central portion of the sheet contains several lamination layers while the edge portions comprise one or several laminated layers which extend across the entire width of the sheet. Corbett produces a multi-layered sheet having multiple layers of different polymers in the center portion of the sheet and only a single polymer at the edge portion of the sheet. The upper limit on the number of layers produced by the multi-manifold dies disclosed by Corbett is typically three or at most four.
U.S. Pat. No. 3,448,183 to Chisholm discloses a method and apparatus for producing a multi-layer film wherein one of the layers is found only in the central portion of the sheet and at least one layer extends across the entire width of the sheet such that the edges of the sheet are composed of a single material. This method and apparatus also utilizes a multi-manifold die which is limited to the production of a sheet material having three or at most four layers.
U.S. Pat. No. 3,397,428 to Donald discloses a method and apparatus for producing a multi-layered sheet having at least two components which are generally concentrically arranged. This concentric arrangement results in the encapsulation of one material by the other resulting in a sheet having a multi-layered construction in the central portion and a single material construction at the edges of the sheet.
U.S. Pat. No. 3,423,498 to Lefevre; U.S. Pat. No. 3,479,425 to Lefevre et al; U.S. Pat. No. 3,415,920 to Lee et al; U.S. Pat. Nos. 4,152,387 and 4,197,069 to Cloeren; and U.S. Pat. No. 3,477,099 to Lee et al disclose other methods and apparatus for the production of laminated films.
There has been a need in the art for an apparatus and method for making a multi-layered sheet material having multiple layers in the center portion of the sheet and a single material at the edges of the sheet, wherein the widths of the center and edge portions may be accurately controlled and varied.
Furthermore, there has been a need in the art for a method and apparatus for producing a laminated sheet having a central portion composed of multiple layers of different materials and at least one edge portion composed of a single material, different from any one of the materials used in the central portion of the sheet.
There has been a still further need in the art for a method and apparatus for producing a laminated sheet material having multiple layers in the central portion of the sheet and edge portions composed of a single material, wherein the multi-layered central portions of the sheet have two or more layers and preferably have more than four layers.